The invention relates to a shapable material, having particular suitability as a bone replacement material, and to shaped articles obtainable therefrom.
In the course of surgical operations the surgeon frequently is faced with the problem of repairing natural bone defects or bone defects caused in the course of an operation. As bone replacement material, there are primarily used "bioinert" or "bioactive" materials known by such terms as "bioceramics", "bioglasses" and "bioglass ceramics". "Bioinert" in this context has been used to describe materials that do not trigger any tissue reaction and that do not release any alien substances. Implants having on their surface a layer of titanium oxide, which functions as a bioinert layer can be included in the bioinert group of materials. "Bioactive" in today's language usage is used to describe materials having the property of directly accreting with bone tissue. They include bioglasses and bioglass ceramics having on the surface distinct proportions of calcium phosphate ceramics, e.g., hydroxyl apatite ceramics and tricalciumphosphate ceramics. As bone replacement material, various hydroxyl apatite ceramics and tricalciumphosphate ceramics are employed which are available on the market in granulated form and as prefabricated shaped parts. The preparation of the materials involves rather expensive sinter processes in which micro and macro porosities are obtained by applying heat and using certain additives.
Furthermore, for remedying bone defects, it has been known to use implantation materials of polyacrylates with filler particles on the basis of tricalcium phosphate (German Offen. 33 25 111) German Offen 33 25 111 also describes that it may be advantageous to add further physiologically tolerable resorptive substances besides tricalcium phosphate, wherein resorption produces porosity on the surface of the replacement material, thus facilitating the accretion of bone material.
German Offen. 27 52 297 similarly describes filled polymethyl methacrylate materials containing carbonates and phosphoric acid, besides a resorbable filler, e.g., Na.sub.2 HPO.sub.4. By joint action of phosphoric acid and carbonate, a porous structure of material is formed when they are mixed (after foaming). Since the materials contain liquid monomers and phosphoric acid, they are not harmless under a toxicological aspect. Moreover, high temperatures may occur in the course of the hardening reaction whereby neighboring tissue may be destroyed. In view of this fact a "bioactive" effect is hardly possible.
In the areas of dentistry so-called "glassionomer cements" have been used. These are reaction products of an aluminum fluorosilicate glass powder and a water-soluble polycarboxylic acid and water. These materials are used primarily as tooth filling material, i.e., dental cement material; they are also used as bone cement, i.e. for anchoring dentures in the bone (e.g., German Offen. 29 29 121).